The received file is larger then the sent file

This is the code that sends the file:

byte[] data = FileUtils.readFileToByteArray(new File("my_file.docx"));

System.out.println(data.length); // prints 6408

ResponseEntity<byte[]> responseEntity = makeResponse(data, HttpStatus.OK, DOCX);

return responseEntity;


private <T> ResponseEntity<T> makeResponse(T responseParameter, HttpStatus httpStatus,
                                           DocumentFormat documentFormat) {
    HttpHeaders headers = new HttpHeaders();

    String filename;

    switch (documentFormat) {
        case PDF:
            headers.setContentType(MediaType.parseMediaType("application/pdf"));
            filename = "output.pdf";
            break;
        case DOCX:
            headers.setContentType(MediaType.parseMediaType("application/docx"));
            filename = "output.docx";
            break;
        default:
            throw new IllegalArgumentException(documentFormat.name() + "is not supported");
    }

    headers.setContentDispositionFormData(filename, filename);
    return new ResponseEntity<>(responseParameter, headers, httpStatus);
}

The received file is of size 8546 bytes. The sent file is of size 6408 bytes. Even if the encoding is somehow wrong, the received file should be of the same size, right? The internals of the received file look like two pages of some random characters, "UEsDBBQACAgIANqVt0YAAAAAAAAAAAAA" <- something like this.

I tried to write the byte array that i have read from my_file.docx to a file on my local disk before sending the response and it works ok.

I also tried to setContentLength of the header i'm sending, but it yields the same result - wrong contents of the received file, even though the size is correct.

Any idea where the additional 2Kb are from? And how do i fix this error?